A session initiation protocol (SIP) event notification system as disclosed in Request for Comments (RFC) 3265 includes a network architecture that permits SIP nodes to request notifications from remote nodes which indicate whether certain events (e.g., change in state information) have occurred in a given end node. Namely, SIP entities may subscribe to the state of a resource associated with a remote node (e.g., a watched subscriber or resource entity), and a notifier node/server associated with the remote node can send a notification if a state change occurs. For example, a SIP entity may send a SIP SUBSCRIBE message to request a SIP event subscription (e.g., a presence state subscription) to a notifier node that services the end node. A notifier node associated with the end node may then be configured to return the current state information (e.g., presence state information) of the node (and updates to the state information) up until the subscription expires. Notably, the SIP events model is a “softstate” model where subscriptions are not permanent and are configured to expire after a predefined amount of time and must be renewed by subsequent subscription (e.g., SIP SUBSCRIBE) messages.
In addition to providing SIP event information associated with watched subscribers or resources, a notifier node/server can also be adapted to provide watcher information (WINFO) to the watched subscriber or resource entity. Problems arise, however, in scenarios where multiple SIP event servers (e.g., presence state servers) are deployed to handle subscription request transactions related to a watched subscriber entity. Namely, responding to watcher information requests become difficult because there isn't a single SIP event server (e.g., a presence server) that has a complete view of all watcher entities that are subscribed to a particular watched entity. In short, multiple SIP event servers may be handling the subscription request transactions related to a single watched subscriber entity. This is particularly problematic because current specifications typically do not allow a watched subscriber entity to discover and contact the full set of servicing SIP event servers in order to acquire all of the watcher subscriber information associated with that requesting watched subscriber entity.
Accordingly, there exists a need for improved methods, systems, and computer readable media for providing SIP event watcher entity information in a communications network.